Farmers use greenhouses to extend the growing season. A greenhouse traps heat. Days that are too cool for a growing plant can be made to be just right. Similar to a greenhouse, greenhouse gases in the atmosphere keep Earth warm.

The Greenhouse Effect

When sunlight heats Earth’s surface, some of the heat radiates back into the atmosphere. Some of this heat is absorbed by gases in the atmosphere. This is the
greenhouse effect
, and it helps to keep Earth warm. The greenhouse effect allows Earth to have temperatures that can support life.

Gases that absorb heat in the atmosphere are called
greenhouse gases
. They include carbon dioxide and water vapor. Human actions have increased the levels of greenhouse gases in the atmosphere (
Figure
below
). The added gases have caused a greater greenhouse effect. How do you think this affects Earth’s temperature?

Human actions have increased the natural greenhouse effect.

Like a blanket on a sleeping person, greenhouse gases act as insulation for the planet. The warming of the atmosphere is because of
insulation
by greenhouse gases. Greenhouse gases are the component of the atmosphere that moderate Earth’s temperatures.

Different greenhouse gases have different abilities to trap heat. For example, one methane molecule traps 23 times as much heat as one CO
2
molecule. One CFC-12 molecule (a type of CFC) traps 10,600 times as much heat as one CO
2
. Still, CO
2
is a very important greenhouse gas, because it is much more abundant in the atmosphere.